Effect of chromophore-chromophore electrostatic interactions in the NLO response of functionalized organic-inorganic sol-gel materials

摘要

In the last years, important non-linear optical results on sol-gel andpolymeric materials have been reported, with values comparable to those foundin crystals. These new materials contain push-pull chromophores eitherincorporated as guest in a high Tg polymeric matrix (doped polymers) or graftedonto the polymeric matrix. These systems present several advantages; howeverthey require significant improvement at the molecular level - by designingoptimized chromophores with very large molecular figure of merit, specific toeach application targeted. Besides, it was recently stated in polymers that thechromophore-chromophore electrostatic interactions, which are dependent ofchromophore concentration, have a strong effect into their non-linear opticalproperties. This has not been explored at all in sol-gel systems. In this work,the sol-gel route was used to prepare hybrid organic-inorganic thin films withdifferent NLO chromophores grafted into the skeleton matrix. Combining amolecular engineering strategy for getting a larger molecular figure of meritand by controlling the intermolecular dipole-dipole interactions through both:the tuning of the push-pull chromophore concentration and the control of TEOS(Tetraethoxysilane) concentration, we have obtained a r33 coefficient around 15pm/V at 633 nm for the classical DR1 azo-chromophore and a r33 around 50 pm/Vat 831 nm for a new optimized chromophore structure.